Re: [Caml-list] Question about register_global_root

[Damien Doligez <Damien.Doligez@inria.fr>]

On Sunday, June 1, 2003, at 12:50 PM, Maas-Maarten Zeeman wrote:

>  Chris Hecker wrote:
>
>>
>>>  handlers = (value *) malloc(sizeof(value));
>>>  register_global_root(handlers);
>>
>>
>> Shouldn't you init *handlers to Val_unit before calling 
>> register_global_root() as well?
>
> The manual explicitly tells that register_global_root should be called 
> before any valid value is stored in it for the first time, like 
> Val_unit. See Rule 4 of Interfacing C with Objective Caml in the 
> manual.
>
> So I think it is ok the way it is implemented.

I'm afraid Chris is right and the manual is wrong.

You can store Val_unit before you call register_global_root, because
Val_unit is not a pointer into the Caml heap.
You must store a valid value before the first allocation that follows
register_global_root.
You can store an allocated value (a pointer into the Caml heap) before
or after calling register_global_root, but it must be after the last
allocation that precedes register_global_root, and before the first
allocation that succeeds it.

At any rate, storing Val_unit before you call register_global_root is
safe and does not cost much CPU time.

-- Damien

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